- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄373919 > AD7843ARQ (ANALOG DEVICES INC) Touch Screen Digitizer PDF資料下載
參數(shù)資料
| 型號(hào)： | AD7843ARQ |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 消費(fèi)家電 |
| 英文描述： | Touch Screen Digitizer |
| 中文描述： | SPECIALTY CONSUMER CIRCUIT, PDSO16 |
| 封裝： | MO-137AB, QSOP-16 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大小： | 193K |
| 代理商： | AD7843ARQ |
第1頁(yè)第2頁(yè)第3頁(yè)第4頁(yè)第5頁(yè)第6頁(yè)第7頁(yè)第8頁(yè)第9頁(yè)當(dāng)前第10頁(yè)第11頁(yè)第12頁(yè)第13頁(yè)第14頁(yè)第15頁(yè)第16頁(yè)
REV. 0
AD7843
–10–
Touch Screen Settling
In some applications, external capacitors may be required across
the touch screen to filter noise associated with it, e.g., noise
generated by the LCD panel or backlight circuitry. The value of
these capacitors will cause a settling time requirement when the
panel is touched. The settling time will typically show up as a
gain error. There are several methods for minimizing or elimi-
nating this issue. The problem may be that the input signal, or
reference, or both, have not settled to their final value before the
sampling instant of the ADC. Additionally, the reference voltage
may still be changing during the conversion cycle. One option is
to stop, or slow down the DCLK for the required touch screen
settling time. This will allow the input and reference to stabilize
for the acquisition time. This will resolve the issue for both
single-ended and differential modes.
The other option is to operate the AD7843 in differential mode
only for the touch screen, and program the AD7843 to keep the
touch screen drivers ON and not go into power-down (PD0 =
PD1 = 1). Several conversions may be required depending on
the settling time required and the AD7843 data rate. Once the
required number of conversions have been made, the AD7843
can then be placed in a power-down state on the last measure-
ment. The last method is to use the 15 DCLK cycle mode, which
maintains the touch screen drivers ON until it is commanded to
stop by the processor.
Reference Input
The voltage difference between +REF and –REF (see Figure 4)
sets the analog input range. The AD7843 will operate with a
reference input in the range of 1 V to V
CC
. The voltage into
the V
REF
input is not buffered and directly drives the capaci-
tor DAC portion of the AD7843. Figure 5 shows the reference
input circuitry. Typically, the input current is 8
μ
A with V
REF
=
2.5 V and f
SAMPLE
= 125 kHz. This value will vary by a few
microamps, depending on the result of the conversion. The
reference current diminishes directly with both conversion rate
and reference voltage. As the current from the reference is
drawn on each bit decision, clocking the converter more quickly
during a given conversion period will not reduce the overall
current drain from the reference.
V
REF
ADC
3-TO-1
MUX
X+
Y+
Figure 5. Reference Input Circuitry
When making touch screen measurements, conversions can be
made in the differential (ratiometric) mode or the single-ended
mode. If the SER/
DFR
bit is set to 1 in the control register, a
single-ended conversion will be performed. Figure 6 shows the
configuration for a single-ended Y coordinate measurement.
The X+ input is connected to the analog to digital converter,
the Y+ and Y– drivers are turned on and the voltage on X+ is
digitized. The conversion is performed with the ADC refer-
enced from GND to V
REF
. The advantage of this mode is that
the switches that supply the external touch screen can be turned
off once the acquisition is complete, resulting in a power saving.
However, the on-resistance of the Y drivers will affect the input
voltage that can be acquired. The full touch screen resistance
may be in the order of 200
to 900
,
depending on the manu-
facturer. Thus if the on-resistance of the switches is approximately
6
,
true full-scale and zero-scale voltages cannot be acquired
regardless of where the pen/stylus is on the touch screen.
Note: The minimum touch screen resistance recommended for
use with the AD7843 is approximately 70
.
X+
Y
–
Y+
+V
CC
GND
IN
–
REF
–
IN+ ADC CORE
REF+
V
REF
IN+
Figure 6. Single-Ended Reference Mode (SER/
DFR
= 1)
In this mode of operation, therefore, some voltage is likely to be
lost across the internal switches and, in addition to this, it is
unlikely that the internal switch resistance will track the resis-
tance of the touch screen over temperature and supply, providing
an additional source of error.
The alternative to this situation is to set the SER/
DFR
bit low.
If one again considers making a Y coordinate measurement,
but now the +REF and –REF nodes of the ADC are connected
directly to the Y+ and Y– pins, this means the analog to digital
conversion will be ratiometric. The result of the conversion will
always be a percentage of the external resistance, independent of
how it may change with respect to the on-resistance of the internal
switches. Figure 7 shows the configuration for a ratiometric Y
coordinate measurement. It should be noted that the differential
Table I. Analog Input, Reference, and Touch Screen Control
A2
1
A1
1
A0
1
SER/
DFR
Analog In
X Switches
Y Switches
+REF
2
–REF
2
0
0
1
1
0
1
1
0
1
0
1
0
0
1
1
0
1
0
1
1
0
1
1
1
1
0
0
0
X+
IN3
Y+
IN4
X+
Y+
Outputs Identity Code, 1000 0000 0000
OFF
OFF
ON
OFF
OFF
ON
ON
OFF
OFF
OFF
ON
OFF
V
REF
V
REF
V
REF
V
REF
Y+
X+
GND
GND
GND
GND
Y–
X–
NOTES
1
All remaining configurations are invalid addresses.
2
Internal node – not directly accessible by the user.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| AD7843ARU | Touch Screen Digitizer |
| AD7843ARU-REEL7 | Touch Screen Digitizer |
| AD7843ARQ-REEL | Touch Screen Digitizer |
| AD7843ARQ-REEL7 | Touch Screen Digitizer |
| AD7845 | LC2MOS Complete 12-Bit Multiplying DAC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AD7843ARQ-REEL | 制造商:Analog Devices 功能描述:TOUCH SCREEN DIGITIZER 制造商:Rochester Electronics LLC 功能描述:2.7V 12-BIT TOUCH SCREN DIGITIZER I.C. - Tape and Reel |
| AD7843ARQ-REEL7 | 制造商:Analog Devices 功能描述:TOUCH SCREEN DIGITIZER 制造商:Rochester Electronics LLC 功能描述:2.7V 12-BIT TOUCH SCREN DIGITIZER I.C. - Tape and Reel |
| AD7843ARQZ | 功能描述:IC ADC 12BIT TOUCHSCREEN 16-QSOP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 觸摸屏控制器 系列:- 標(biāo)準(zhǔn)包裝:96 系列:- 類型:- 觸摸面板接口:- 輸入數(shù)/鍵:- 分辨率（位）:- 評(píng)估套件:* 數(shù)據(jù)接口:- 數(shù)據(jù)速率/采樣率 (SPS，BPS):- 電壓基準(zhǔn):- 電源電壓:- 電流 - 電源:- 工作溫度:- 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:帶卷 (TR) |
| AD7843ARQZ2 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Touch Screen Digitizer |
| AD7843ARQZ-REEL | 功能描述:IC ADC 12BIT TOUCHSCREEN 16-QSOP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 觸摸屏控制器 系列:- 標(biāo)準(zhǔn)包裝:96 系列:- 類型:- 觸摸面板接口:- 輸入數(shù)/鍵:- 分辨率（位）:- 評(píng)估套件:* 數(shù)據(jù)接口:- 數(shù)據(jù)速率/采樣率 (SPS，BPS):- 電壓基準(zhǔn):- 電源電壓:- 電流 - 電源:- 工作溫度:- 安裝類型:表面貼裝 封裝/外殼:16-TSSOP（0.173"，4.40mm 寬） 供應(yīng)商設(shè)備封裝:16-TSSOP 包裝:帶卷 (TR) |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。